JPS5936870B2 - Composite coated steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite coated steel sheet with excellent workability and corrosion resistance. More specifically, the present invention relates to a composite coated steel sheet with excellent workability and corrosion resistance. The first layer consists of an ultra-thin pre-plated layer of chromium, nickel and zinc), and the second layer consists of zinc powder or zinc alloy powder and organic resin (if necessary, scaly aluminum powder is added) The purpose is to provide a composite coated steel sheet with a third layer of organic resin coating, which has excellent corrosion resistance and workability, has a uniform coating, and can be easily and continuously produced in large quantities. The object of the present invention is to provide an extremely economical composite coated steel sheet.

Conventionally, hot-dip galvanized steel sheets and electrogalvanized steel sheets have been used as base steel sheets for painting.

However, although hot-dip galvanized steel sheets have relatively excellent corrosion resistance, pretreatment for painting is difficult, and they are inferior in paintability and workability. On the other hand, electrogalvanized steel sheets are easy to paint,
Both have excellent workability, but there was a problem with corrosion resistance when used in a severely corrosive atmosphere. Therefore, as an improvement measure when using an electrogalvanized steel sheet as a base steel sheet for painting, it is necessary to coat it with several micrometers of undercoating paint containing mainly chromic acid-based rust-preventing pigments, and then apply a coating of specifications according to the purpose on top of that. It has been used with a top coat. However, this measure did not yield satisfactory results, and when put into practical use,
It often caused trouble. For example, an electrogalvanized steel sheet with a plating amount of 5y/771" is coated with a zinc-based linoate film of 2V/m", and is further coated with 20V/m" of chromium.
~ / Let's talk about a painted steel plate that uses 77L'' chromate treatment as the base steel plate for painting.An epoxy base paint (containing a chromic acid rust-preventing pigment) is applied to the base steel plate for painting. Furthermore, the antirust effect of a coated steel sheet coated with a polyester topcoat is largely due to the chromic acid antirust pigment contained in the undercoat.

To explain this rust prevention effect in more detail, the corrosion resistance when a 5 μm thick film is formed with an undercoat that does not contain a chromic acid-based rust preventive material and then the polyester topcoat is applied is determined by a salt spray test according to JIS Z237L. ,
Red rust formed on the cross cut portions after 25 hours, but with the above-mentioned coated steel sheet containing 4% (by weight, the same applies hereinafter) of a chromic acid-based rust preventive pigment in the undercoat, red rust formed on the cross cut portions for 200 hours and on the flat plate portions. Rust was finally observed after 40.0 hours, which was approximately 8 times more effective.
However, when the above two samples were exposed outdoors, the effect of the chromic acid-based rust-preventing pigment was about 1.3 times, and the painted steel sheet, which is highly dependent on the chromic-acid-based rust-preventing pigment, had improved corrosion resistance. This shows that the results are insufficient and there are practical problems. Regarding the rust prevention effect when no top coat is applied, that is, when only the undercoat is applied, the effect of the chromic acid-based rust preventive pigment is almost the same as above, apart from the decrease in corrosion resistance due to no top coat. It shows the trend of

On the other hand, recently developed zinc-based paints, or zinc-rich paints, are known for the purpose of rust-preventing steel materials. For applications requiring corrosion resistance, the mixture is applied to a steel plate by roll coating, knife coating, spray coating, or dipping, and then hardened by drying or baking. The effect cannot be obtained unless a coating film with a thickness of 40 μm or more is formed.

Here, if the coating film has a thickness of 40 μm or more, the coating will peel off at the processed portion during the forming process of the steel plate, and the effect of zinc-rich paint will be lost. However, if the film thickness is 40 μm or less, the rust prevention effect is low and there is a problem, and if the zinc powder content in the film is reduced to 50% or less, workability is improved, but this Such zinc-rich paints rapidly reduce their rust-preventing effect and cannot achieve the desired rust-preventing effect. In short, zinc-rich paint cannot be used in applications where molding is performed after painting, and it has been difficult to put it to practical use in this respect. Therefore, the present invention investigates the correlation between the effectiveness of the undercoat paint on electrogalvanized steel sheets in salt spray tests and outdoor exposure tests.
We are conducting research on coated steel sheets with zinc or zinc-based metal plating, applying an undercoat containing zinc powder or zinc alloy powder, and then coating the steel sheets with zinc or zinc-based metal plating. This is a completed composite coated steel sheet in which an organic resin coating is further formed.

To explain in detail the contents of the present invention, the plating amount of zinc or a metal whose main component is zinc, which is the first layer, is 1 to 1.
The appropriate amount is 40y/ml.

The amount of plating is related to the content of zinc powder or zinc alloy powder in the second layer coating and the coating thickness, but a minimum of 17/I is required. When it is less than 1f7/Trl, the corrosion resistance deteriorates rapidly.

This is thought to be because the steel sheet is not fully covered with zinc or a metal whose main component is zinc. Incidentally, even if the plating amount becomes 407/Trl or more, the corrosion resistance is not improved in spite of the increase, which is uneconomical and disadvantageous.
In addition, when forming the first layer, known pre-plating, such as tin pre-plating, chrome pre-plating, and nickel pre-plating, is applied to further improve the corrosion resistance of the first layer, resulting in a composite coating. It is also possible to impart favorable corrosion resistance to the steel plate. For example, tin front plating treatment as shown in Japanese Patent Publication No. 43-26723, chrome front plating treatment as shown in Japanese Patent Publication No. 44-25882, or Japanese Patent Publication No. 44-25882.
By performing a nickel pre-plating treatment as shown in No. 4-28564 and further a zinc pre-plating treatment, an extremely thin pre-plating layer of less than 37/wl can be formed. Although corrosion resistance is improved by forming this pre-plated layer, no adverse effect on workability (tendency to inhibit workability) associated with this is observed.
Here, there may be cases in which a second layer is formed after these pre-plating treatments are performed without performing the main plating treatment, but these also fall within the scope of the composite coated steel sheet of the present invention. Needless to say.

Next, if the particle size of the zinc powder or zinc alloy powder contained in the second layer is 10 μm or less, a dense coating can be obtained, but if it exceeds 10 μm, the uniformity of the coating will be poor, and the upper layer cannot be coated. make sex worse. The amount of metal powder contained in the film is suitably 10 to 95%.

If it is less than 10%, the corrosion resistance will not be sufficient, and if it exceeds 95%, the processing adhesion after film formation will be poor.

In addition, in order to further improve corrosion resistance, the thickness is 2 μm.
The following scaly aluminum powder is added at a ratio of 7% or less.

This aluminum powder is preferably in the form of scales; if it is in the form of granules, the adhesion to the first layer, corrosion resistance, and workability will be poor. If the thickness of the scaly powder is 2 μm or more, it is not expected to improve corrosion resistance much. If the ratio to the film composition exceeds 7%, workability will be extremely reduced, which is not preferable. The second layer is formed by kneading the above metal powder using an organic resin as a binder, applying the mixture, and heating and drying it.

The organic resin includes one or more of acrylic, polyester, polybutadiene, melamine, phenol, epoxy, and urethane resins.
The pigment to be added as necessary may be either organic or inorganic, and a commercially available pigment may be used. The thinner the second layer is, the worse the corrosion resistance tends to be, and the thicker it is, the lower the workability is.

Therefore, the appropriate range is 2 to 20 μm, which is determined by considering the purpose of use and economic efficiency as a composite coated steel sheet.
It is. A top coat is further applied to the upper layer of the second layer thus formed to form a third layer.

As the top coating, a commercially available organic resin coating can be used, but it must be selected with due consideration given to the relationship with the second layer. For example, if the resin used as the binder for the second layer is epoxy, acrylic or polyester is suitable for the top coat. Furthermore, when a vinyl chloride resin paint is used as the top coat, it is necessary to use a material such as acrylic type that has strong adhesive strength with the vinyl chloride resin as the second layer. In any case, the third layer is composed of one or more of acrylic, polyester, polybutadiene, melamine, phenol, epoxy, and vinyl chloride resins.
The baking conditions for forming the third layer vary depending on the purpose of use, in other words, the properties of the paint, etc., but for example, when applying a polyester topcoat of 15 μm as an outdoor wall material, the steel plate thickness is 0.3 m7. ! When the first layer is a 107/I galvanized layer and the second layer is a 5 μm thick coating in L, a baking treatment is performed at an ambient temperature of 270±5° C. for 60 seconds.

In addition, when coating a vinyl chloride film of 200 μm, 2
A baking process is performed for 60 seconds at 30±5°C. In addition,
The thickness of the third layer is not particularly limited, and is determined by considering the purpose of use and economic efficiency of the composite coated steel sheet.

Hereinafter, embodiments of the present invention will be shown and explained in detail.

Example 1 Plating amount 157 on a mild steel plate with a thickness of 0.25
/A electrogalvanizing was applied, and the following second layer coating treatment was performed on the top layer.

Heat Drying Baking Conditions The above-mentioned coated steel plate was processed under baking conditions at a plate temperature of 205±5°C.

The coating film produced by this treatment contains 75% of the coating amount of the second layer.
It contained.

Further, on top of the above treatment, a polyester paint was applied as a third layer to a thickness of 12 μm. The corrosion resistance of the obtained composite coated steel sheet of the present invention was 7 in the salt spray test according to JIS Z237l.
Even after 50 hours had passed, there was no red rust on the end faces and crosscuts. Regarding Blister 1, the occurrence was observed after 100 hours had elapsed. In addition, Eriksen overhang (7mT
IL), Dupont impact (12.7m77!φ, 50CW
The adhesion test by L, 1k9) was also good. On the other hand, a commercially available epoxy paint containing 3% strontium chromate was applied as a second layer to the above-mentioned 15 f/wl galvanized steel sheet, and a third layer of the same polyester paint as above was applied. In the comparative example, red rust was observed after 300 hours, and blisters were observed after 70 hours. In addition, as a result of outdoor exposure of each sample,
In the composite coated steel sheet of the present invention, no red rust or blisters were observed even after 18 months, but in the comparative example, red rust was observed after 12 months, but the second layer was omitted. Red rust appeared on the item after 10 months. Example 2 A mild steel plate similar to Example 1 was plated with a metal containing zinc as the main component (according to the treatment based on the example in Japanese Patent Publication No. 49-19979) at 10 V/I to form the second and third layers. Example 1
The same treatment was applied.

The corrosion resistance of the obtained composite coated steel sheet of the present invention is JISZ2
Even after 750 hours in the salt water spray test using 37 liters, no red rust was observed on the end faces and crosscuts. As for Blister 1, it could not be recognized even after 500 hours had passed. In addition, Eriksen overhang (7711!), Dubon impact (12.7 dia.
, 50 cm, 11 kg) was also good.
Example 3 A mild steel plate similar to that of Example 1 was electrogalvanized with a 17/I coating, and the following composite treatment coating was applied as a second layer.

Heat Drying Baking Conditions The above-mentioned coated steel plate was treated under heating conditions at a plate temperature of 215±5°C.

The paint film resulting from this treatment contained 35% of the amount of metal in the second layer.

Furthermore, a third layer of commercially available acrylic paint was applied thereon. The corrosion resistance of the obtained composite coated steel sheet of the present invention is as follows:
5 in the salt water spray test according to JIS Z237l mentioned above.
No red rust was observed even after 00 hours had passed. Also, Eriksen overhang (711), Dupont impact (12.
The adhesion test using 7m1Lφ, 500frL11kg) was also good. Example 4 Example 2 with a plating amount of 207/d on a mild steel plate with a thickness of 0.5 mm
Electroplated with a metal whose main component is zinc, similar to
The following coating was applied.

Heat drying baking conditions The above paint was heat treated in an atmosphere of 250°C for 60 seconds.

The second layer coating obtained by this treatment contained 70% of the metal content of the second layer coating.

Then, it was coated with 200 μm of vinyl chloride, and the atmosphere was kept at 230°C.
Heat treatment was performed for x60 seconds. As for the corrosion resistance of the composite coated steel sheet of the present invention, no red rust was observed even after 300 hours and no blisters were observed after 750 hours in a salt spray test according to JIS Z237L.

In addition, Eriksen overhang (7mm), Dupont impact (
The adhesion test using 12.7 mmφ, 50 cm, 11<g) was also good. On the other hand, the second layer of paint from which zinc powder and aluminum powder were removed developed red rust after 200 hours.

Example 5 A mild steel plate similar to Example 1 was coated with 15y/M as in Example 1.
Zinc No. 2 was electroplated and the second layer was processed as described below.

Suspension Composition Heating Drying Baking Conditions The above-mentioned coated steel plate was processed under baking conditions at a plate temperature of 205±5°C.

The coating of paint from this treatment contained 15% of the coating weight of the second layer of metal.

Furthermore, a 15 μm thick polyester paint was applied thereon as a third layer. The corrosion resistance of the obtained composite coated steel sheet of the present invention was excellent as in Example 1, and was JISZ23
In the salt water spray test using 7 liters, no red rust was observed even after 350 hours. Also, Eriksen overhang (7J mo V! m), Dupont impact (12.7mmφ, 50
(V7!, kg) was also good.
Example 6 A mild steel plate similar to Example 1 was pre-plated with tin at 0.3 V/m", then metal plating with zinc as the main component similar to Example 2 was applied at 10 y/Trl, and The same treatment as in Example 1 was applied to the third layer and the third layer.

The corrosion resistance of the obtained composite coated steel sheet of the present invention was determined by the above-mentioned JI
In the salt spray test using SZ237l, no red rust was observed on the end faces and crosscuts even after 800 hours.

As for blistering, no blisters were observed even after 600 hours. Also, Eriksen overhang (7
mm), Dupont impact (12.7mmφ, 50cm)
The adhesion test according to 1k9) was also good.

Claims (1)

[Scope of Claims] 1. A plating layer of zinc or a metal containing zinc as a main component with a metal plating amount of 1 to 40 g/m^2 on the surface of a mild steel plate, or a known pre-plated layer below the metal plating layer. A metal plating layer (hereinafter referred to as the first layer) with a plating layer, and the upper layer,
One or more types of zinc grains or zinc alloy powders with a film thickness of 2 to 20 μm and a particle size of 10 μm or less, or this with a thickness of 2 μm
Metal powder with the following scaly aluminum powder added is 10
~95% by weight (however, when scaly aluminum powder is added, the amount is 7% by weight or less), the balance being acrylic,
A metal powder coating layer (hereinafter referred to as the second layer), which is a binder whose main component is one or more of polyester, polybutadiene, melamine, phenol, epoxy, and urethane resins, and an upper layer thereof. A resin coating (hereinafter referred to as the third layer) whose main component is one or more of acrylic, polyester, polybutadiene, melamine, phenol, epoxy, and vinyl chloride resins.
A composite coated steel plate having. 2. The composite coated steel sheet according to claim 1, wherein the pre-plated layer is tin, chromium, nickel or zinc with a thickness of 3 g/m^2 or less.